AU2012250293A1

AU2012250293A1 - Free Flow Fertilisers

Info

Publication number: AU2012250293A1
Application number: AU2012250293A
Authority: AU
Inventors: Terrence John Smith
Original assignee: BALLANCE AGRI NUTRIENTS Ltd
Current assignee: BALLANCE AGRI-NUTRIENTS Ltd
Priority date: 2005-09-06
Filing date: 2012-11-16
Publication date: 2012-12-06

Abstract

A process for producing a free flow granular, prill or other solid form ("granular") material, comprising or including the steps of (i) slurry blending fine urea with a water soluble phosphate, 5 (ii) adding one or more of the group consisting of calcium oxide and metal oxides, (iii) adding a granular material to be coated whilst the result of step (ii) is still a slurry, and (iv) adding and/or mixing a particulate material to and/or with the result of step (iii) to provide the free flow granular material.

Description

2 The present invention relates to fertilisers. Urea (usually granular urea) is used as a fertiliser owing to its high nitrogen content. It has long been recognised however that urea can benefit from coating. It has also been recognised that when coating urea to enhance its efficacy as a fertiliser when applied to crops or 5 pasture that there is the prospect of having combined with the urea other nutrient materials. New Zealand Patent Application No. 227757 of Hi-Fert Pty Ltd relates to a process for producing a granular fertiliser where particles of a base fertiliser selected from ortho phosphates of calcium, ammonium and potassium, and mixtures thereof, are subjected to a coating sequence of an inner and outer layer. The outer layer comprises (i) elemental sulphur and (ii) a 10 supplemental micro-nutrient and, if the inner layer consists of water only, (iii) 0.1 to 10% (by weight of the total composition) of a salt selected from the group consisting of water soluble sulphates and phosphates of ammonium or potassium, sulphates of metallic trace of elements, and mixtures thereof. When the inner layer is not purely water it may be an aqueous solution of the salt selected from the group of sulphates and phosphates of ammonium or potassium and 15 mixtures thereof. Such a procedure does not extend to a base fertiliser which is granular urea. New Zealand Patent specification 286023 of Hi-Fert Pty Ltd discloses a process for the production of nutrient-coated urea fertiliser by the addition of one or more nutrient(s) and/or secondary nutrient(s) to particulate urea fertiliser. That process involves particulate urea being tumbled in a conventional coating device in the presence of merely sufficient water to render the 20 surface of the urea granules tacky for the particulate micronutrient(s) and/or secondary nutrient(s) and/or chemical compound(s) added as coating additive(s) to assist the coating and bonding mechanism. The resultant product is urea with a nutrient-coating comprising one or more hydrated reaction products on the particulate urea. No aqueous binder is used. Nor is any subsequent drying step required. 25 New Zealand Patent specification 330993 of Hi-Fert Pty Ltd relates to a process for incorporating plant nutrients as components of a semi-permeable coating of a granular phosphatic or non phosphatic fertiliser. The process also includes reducing the rate of dissolution of water soluble nutrients from the fertiliser. The process is stated as forming in situ "and without addition of phosphoric acid" on the surface of the granules of the fertiliser, a 30 coating comprising one or more ammonium magnesium phosphate and/or potassium magnesium phosphate compounds. New Zealand Patent 330993 discloses as a preferred granular fertiliser a phosphatic fertiliser with coating components comprising magnesium oxide or magnesium hydroxide. The coating operation of NZ330993 involves providing in a granulating device a bed of 35 granules into which is then mixed the coating components (e.g. a phosphatic fertiliser and either 3 MgO or Mg(OH)). The amount of water used in the coating procedure is (as in NZ 286023) appears to be "merely sufficient" (to 1.7% w/w of water is stated as preferred in the mix). Hi-Fert Pty Ltd New Zealand Patent Application No. 334428 relates to a method of producing a fertiliser coated with a coating incorporating elemental sulphur where the base 5 fertiliser is a granular phosphate containing or sulphate containing fertiliser. The steps of the method comprise (a) placing granules of such a base fertiliser in a mixing-cum-coating device, (b) adding water or an aqueous solution comprising soluble plant nutrient(s), and (c) adding a mixture of sulphur and a coating additive selected from calcium oxide, 10 calcium hydroxide and calcium sulphate. The base fertiliser of such a method does not extend to urea. New Zealand Patent Specification 511606 of Summit-Quinphos (NZ) Limited relates to urea coated with sulphur. There the coating procedure involves special characteristics of wet ground sulphur as the medium by which the micro-nutrient sulphur is adhered to the urea 15 granule. The present invention as an alternative to such procedures recognises as an object considerable advantage to be derived from coating urea and blending such coated urea with superphosphate. The present invention also or alternatively sees as an object an advantage in being able 20 to utilise in the coating process a superphosphate dust together with other nutrient additives. It is another or alternative object of one embodiment of the present invention to provide a coating process for urea suitable to utilise superphosphate dust preferably thereby to create a coated urea which can withstand high humidity without developing stickiness and/or which can be blended in any proportion with, by way of example, a superphosphate, (e.g. such as 25 fresh, hot single superphosphate). It is an additional or alternative object of the present invention to incorporate calcium oxide and/or magnesium oxide such as calcined magnesium oxide with the urea. This is despite the aforesaid New Zealand Patent Specification 286023 indicating that calcined or high temperature MgO cannot be employed in the coating operation (page 12, line 25). 30 It is also an additional or alternative object to provide a high urea (e.g. 75 to 85% w/w) coated urea fertiliser, for example, able to be easily blended with single super phosphate (SSP).

4 In an aspect the invention is a process for producing a free flow granular, prill or other solid form ("granular") material, comprising or including the steps of (i) slurry blending fine urea with water soluble phosphate (e.g. fine superphosphate), (ii) adding one or more of the group consisting of calcium oxide and metal oxides, 5 (iii) adding a granular material to be coated whilst the result of step (ii) is still a slurry, and (iv) adding and mixing a particulate material to the result of step (iii) to provide the free flow granular material. Many suitable water soluble phosphates can be used including superphosphates 10 (whether single, double, triple superphosphate, whether serpentine phosphates or other). Optionally the soluble phosphate is a fine superphosphate (e.g. a single superphosphate). Optionally step (i) can include other material(s). 15 Preferably the other material(s) is (are) selected from the group consisting of sulphur, DCD and NBPT. Preferably step (ii) involves CaO and/or MgO. Optionally the granular material of step (iii) is or includes urea. Optionally step (iii) does not involve urea. 20 Preferably the granular material of step (iii) is a fertiliser. Preferably granular material is of or includes one or more of urea, potash, diammonium phosphate and monoammonium phosphate. Preferably in some embodiments the free flow granular material is greater than 50%w/w urea. Preferably the free flow granular material is greater than 65%w/w urea. Preferably the free 25 flow granular material is from 75 to 85%w/w urea. Optionally step (iv) involves using one or more of particulate solids selected from calcium oxide, metal oxide(s), magnesium oxide, fine rock, fine serpentine rock (e.g. ground), fine lime (e.g. ground), fine dolomite (e.g. ground) and fine zeolite (e.g. ground). Preferably step (iv) involves calcium oxide and/or at least one metal oxide. 30 Preferably step (iv) involves CaO and/or MgO. Preferably the particulate material(s) added and mixed by step (iv) comprise from 1 to 15% w/w of the free flow granular material. In another aspect the invention is a free flow granular material prepared by any such process.

5 In an aspect the invention is a process for producing a free flow granular fertiliser (optionally blendable with other particulate fertiliser(s) e.g. with SSP) comprising or including the steps of (i) slurry blending fine urea with fine superphosphate (optionally also with other 5 materials), (ii) adding CaO and/or MgO, (iii) adding granulated urea whilst the result of step (ii) is still a slurry, and (iv) adding and mixing CaO and/or MgO to the result of step (iii) to provide the fertiliser. 10 The "other materials" may be selected from sulphur, DCD and NBPT and can be more than ore said material. Preferably the granular fertiliser is greater than 50% w/w urea (preferably more than 65% w/w). Most preferably urea comprises 75 to 85% w/w of the granular fertiliser. In an aspect the invention is a free flow fertiliser of a core derived from a combination 15 of (a) calcium oxide and/or magnesium oxide with (b) an aqueous slurry of urea and a superphosphate and then mixing granulated urea with the resultant slurry thereby to produce the granular core, the core having been rendered free flow by the preferred but optional addition of calcium oxide and/or magnesium oxide to the core. Preferably the granular fertiliser is greater than 50% w/w urea (preferably more than 20 65% w/w). Most preferably urea comprises 75 to 85% w/w of the granular fertiliser. In another aspect the invention is a fertiliser blend of (i) a first particulate fraction where each particle contains a urea granule and a coating resulting from the use of a slurry that includes and/or has included a superphosphate and urea and at least one of calcium oxide and/or magnesium oxide, 25 and (ii) a second particulate fraction (different from (i)) of at least a superphosphate. Preferably (ii) is SSP and (i) is coated urea. Preferably the granular fertiliser is greater than 50% w/w urea (preferably more than 65% w/w). Most preferably urea comprises 75 to 85% w/w of the granular fertiliser. 30 In another aspect the present invention consists in a process for providing a free flow granular fertiliser, said process comprising mixing an aqueous slurry of urea and at least one superphosphate with calcium oxide and/or magnesium oxide, (optionally heating the mix and/or allowing it to rise in temperature), adding granular urea and thereafter rendering the resultant particulate material free flow by the addition of at least one particulate calcium and/or metal 35 oxide thereto.

6 Preferably the granular fertiliser is greater than 50% w/w urea (preferably more than 65% w/w). Most preferably urea comprises 75 to 85% w/w of the granular fertiliser. And still a further aspect the present invention consists in a method of preparing a granular fertiliser which comprises the steps of mixing an aqueous slurry of urea and at least 5 one superphosphate with calcium oxide and/or magnesium oxide (optionally causing and/or allowing the temperature of the mix to rise) and adding granular urea thereto whilst still a slurry thereby to produce the granular fertiliser. Optionally the resultant granular or particulate material can be rendered free flow by the addition of at least one particulate calcium and/or metal oxide (e.g. MgO) thereto. 10 Preferably the granular fertiliser is greater than 50% w/w urea (preferably more than 65% w/w). Most preferably urea comprises 75 to 85% w/w of the granular fertiliser. We have endeavoured to enhance the usefulness of urea as a fertiliser component in a product that contains more than just urea. We have determined that it is possible to coat urea with superphosphate dust by 15 working the urea, coating the dust to the sticky urea and then drying the material while moving to prevent its clumping. Once dried, the dust coated urea stayed dried and the coating was well adhered. Subsequent testing showed that the material could withstand subsequent mixing with hot super phosphate (e.g. fresh, hot single superphosphate) and was very resistant to chemical and physical attack which normally plagues urea/superphosphate mixes. Such a procedure 20 however required great care to be exercised to avoid clumping. Since then we have determined that we can slurry together both urea and superphosphate dust and thereafter, by appropriate addition thereto of at least one of a calcium and/or metal oxide (e.g. magnesium oxide), derive a product that can even have made use of calcined or high temperature MgO. The aforementioned New Zealand Patent Specification 25 286023 stated that calcined or high temperature MgO could not be employed in the coating operation of that disclosed prior art procedure. It is our experience that calcined MgO can be used for the coating system and that it is advantageous that MgO is used as a resulting coating is harder and more tenaciously adherent than the coatings without MgO. It has been possible with the process of the present invention 30 for the purpose of blending with SSP of producing a coated urea granular material containing, for example, from 75 to 85% w/w urea. This high urea granular material is prepared preferably using a slurry not believed to have other than urea, calcium sulphates, calcium phosphates, calcium fluoride, silica and a trace of ammonium present. The coating is believed (and we do not wish to be tied to any theory) to have a first layer 35 which is essentially a saturated solution of urea, calcium orthophosphates, calcium sulphate, 7 calcium fluoride and optionally magnesium oxides/hydroxides and calcium oxides/hydroxides or mixtures of both. The coating by X-ray diffraction has the following content: Table 1: Formula Quantity MgO 61 Mg(OH)2 23 CaSO4 8 CaCO3 3 Ca2(HPO4)(SO4)(H20)4 3 CaSO4. 0.5H20 1 Ca(HP04)(H20)2 1 SiO2 trace 5 Such a coating is an incomplete coating but considered as a whole preferably comprises from about 15 to 25% w/w of the coated granular urea product. A preferred procedure of the present invention will now be described with reference to the accompanying drawings in which 10 Figure 1 is a process of the present invention where urea slurry and superphosphate dust slurry is combined with calcium oxide and/or metal oxide(s) (e.g. CaO and/or MgO) and thereafter solid forms (preferably of a fertiliser but not necessarily so) are coated by the slurry product ultimately to produce a free flow product. Figure IA is a flow diagram generic to the methodology of the present invention where 15 the granular material is urea one or both instances using calcium oxide and/or other metal oxide(s) as the optional metal oxide, Figure 2 is the process of Figure 1 coupled to a blending procedure [e.g. with a single superphosphate ("SSP")], Figure 2A is a more specific flow diagram of a preferred embodiment of the present 20 invention as in Figure 1A coupled to a blending procedure with a single superphosphate ("SSP"), Figure 3 is the process of Figure 2 with more specifity and with optional other additives, and Figure 3A shows Figure 2A with more specificity and with optional other additives. A preferred process typified by Figure 1, 2 and 3 [non specific as to solid(s) form(s) to 25 be coated with the slurry and non specific as to the particulate material(s) of the dusting step post mixing to coat evenly] is as follows: 8 An at least nearly saturated solution of urea in water (50% w/w at Room Temperature) is prepared. Superphosphate Dust (<2504m) (preferably slurried) to the Urea solution to achieve a slurry of 25 to 75% solids. This material is stable and may be stored. A metal oxide or metal oxides is (are) then added to the superphosphate/urea/water 5 slurry. Preferably the metal oxide(s) is (are) either calcium oxide, magnesium oxide or a mixture of both. The addition immediately causes the slurry temperature to rise. Immediately granular, prill, powder or other material ("granular material") is then added to the resultant slurry and mixed until coated evenly. Whilst hereafter urea granules are described in some detail, any suitable material can be utilised. By way of example, granular or other 10 particulate forms of fertiliser material or fertiliser including materials can be used. Examples include, but are not limited to, urea, potash, diammonium phosphate, monoammonium phosphate, etc, and/or mixtures thereof. For the step post such mixing a particulate material is, or particulate materials are, then added. Whilst in some forms of the present invention calcium oxide and/or magnesium oxide 15 are used, this need not be the case. Other particulate materials include, by way of example, ground minerals or rocks or, for that matter, any appropriate dry fine particulate solid material that will achieve the free flow outcome as a final step (iv) of the process. Examples include ground serpentine rock, ground lime, ground dolomite, ground zeolite and other such materials. It is preferable that such particulate material(s) added as the stage (iv) should account for 20 from 1 to 15% w/w of the overall free flow granular material. As will be described hereinafter with the more specific procedures in respect of Figures 1A, 1B and 1C, other additions can be included even if the granules added at stage (iii) are not urea and even if the particulate material added at step (iv) is not calcium oxide and/or magnesium oxide. 25 A preferred process typified by Figures 1A, 2A and 3A (i.e. where the solid form(s) is urea granules, prills or the like) is as follows: An at least nearly saturated solution of urea in water (50% w/w at Room Temperature) is prepared. Superphosphate Dust (<2504m) (preferably slurried) to the Urea solution to achieve a slurry of 25 to 75% solids. This material is stable and may be stored. 30 A metal oxide or metal oxides is (are) then added to the superphosphate/urea/water slurry. Preferably the metal oxide(s) is (are) either calcium oxide, magnesium oxide or a mixture of both. The addition immediately causes the slurry temperature to rise. Immediately granular urea is then added to the resultant slurry and mixed until coated evenly. 35 If urea is not added immediately the slurry may harden and become unworkable.

9 Particulate calcium oxide or magnesium oxide, or a mixture of both, is then added to the evenly coated urea and mix until a free flowing granular product is formed. Magnesium and calcium oxides ranging from 100% calcium to 100% magnesium can be added to the mixture until a free flowing granular mixture is achieved. This required between 5 5 and 15% addition (w/w) of metal oxides. The higher the percentage of calcium oxide in the mixture the hotter the mixture became and the faster the drying and hardening process. 100% calcium oxide coatings quickly warmed and the coating dried and hardened within 5 minutes. For mixtures containing high Magnesium oxide content, some heating was needed to initiate the drying process. However, once 50'C was reached the reaction proceeded without the need for 10 additional heating and dried itself within 20 minutes. The resulting product was a urea with a hard, dry coating. Extensions to the procedure aforesaid have allowed the inclusion of Dicyanodiamide (DCD), N-(N-Butyl)thiophosphoric triamide (NBPT marketed as Agrotain), inclusion of Serpentine Superphosphate dust and inclusion of sulphur dust. We have found that 5% by 15 weight of the final product can readily be added as particulate sulphur by inclusion of sulphur dust in the initial slurries. Likewise DCD and NBPT can be added at a similar point in the process without detracting from the resultant coating and to similar levels if desired to that of sulphur. A process in accordance with the present invention has given rise to a coating material 20 having the following analysis and that is table 1. Assessments noted that the coating does not include ammonium magnesium phosphate nor potassium magnesium phosphate compounds nor does it have sulphates and phosphates of ammonium or potassium, nor sulphates of metallic trace elements, or mixtures thereof. Coatings prepared with magnesium oxide and harder and more resistant to abrasion 25 than those prepared with calcium oxide. Coatings prepared with a percentage of calcium oxide developed more heat during preparation and the coatings hardened at a faster rate. Coatings containing superphosphate dust were harder than those with no superphosphate dust. All coatings imparted a resistance to both humidity and reaction with hot fresh superphosphate. For example after 24 hours at 100% humidity the coated products gained less than 5% weight and 30 were still free flowing. By comparison normal urea was almost liquid.

10 Examples of free flow granular material are the result of: Example 1 5% w/w SSP 5% w/w dissolved urea 5% w/w water 75% w/w solid urea 10% w/w MgO Example 2 5% w/w SSP 5% w/w dissolved urea 5% w/w water 60% w/w potash 25% w/w MgO 5

Claims

1. A process for producing a free flow granular, prill or other solid form ("granular") material, comprising or including the steps of (i) slurry blending fine urea with a water soluble phosphate, 5 (ii) adding one or more of the group consisting of calcium oxide and metal oxides, (iii) adding a granular material to be coated whilst the result of step (ii) is still a slurry, and (iv) adding and/or mixing a particulate material to and/or with the result of step (iii) to provide the free flow granular material. 10

2. A process of claim 1 wherein the water soluble phosphate is single superphosphate (SSP).

3. A process of claim 1 or 2 wherein step (i) can include other material(s).

4. A process of claim 3 wherein the other material(s) is (are) selected from the group consisting of sulphur, DCD and NBPT. 15

5. A process of any one of the preceding claims wherein step (ii) involves CaO and/or MgO.

6. A process of any one of the preceding claims wherein the granular material of step (iii) is or includes urea.

7. A process of any one of the preceding claims wherein the granular material of step (iii) is 20 a fertiliser.

8. A process of claim 7 wherein said granular material is of or includes one or more of urea, potash, diammonium phosphate and monoammonium phosphate.

9. A process of claim 7 or 8 wherein the free flow granular material is greater than 50%w/w urea. 25

10. A process of claim 9 wherein the free flow granular material is greater than 65%w/w urea.

11. A process of claim 10 wherein the free flow granular material is from 75 to 85%w/w urea.

12. A process of any one of the preceding claims wherein step (iv) involves using one or 30 more of particulate solids selected from calcium oxide, metal oxide(s), magnesium oxide, fine rock, fine serpentine rock (e.g. ground), fine lime (e.g. ground), fine dolomite (e.g. ground) and fine zeolite (e.g. ground).

13. A process of claim 1 wherein step (iv) involves calcium oxide and/or at least one metal oxide. 35

14. A process of claim 1 wherein step (iv) involves CaO and/or MgO. 12

15. A process of any one of the preceding claims wherein the particulate material(s) added and mixed by step (iv) comprise from 1 to 15% w/w of the free flow granular material.

16. A free flow material produced by any one of the preceding claims or by a process of any one of the accompanying drawings. 5

17. A process for producing a free flow granular fertiliser comprising or including the steps of (i) slurry blending fine urea with fine superphosphate (optionally also with other materials), (ii) adding CaO and/or MgO, 10 (iii) adding granulated urea whilst the result of step (ii) is still a slurry, and (iv) adding and mixing CaO and/or MgO to the result of step (iii) to provide the fertiliser.

18. A process of claim 17 wherein the other materials selected from sulphur, DCD and NBPT are present in step (i). 15

19. A process of claim 17 or 18 wherein the granular fertiliser is greater than 50% w/w urea.

20. A free flow fertiliser of a dusted core, the core having been derived from a combination of (I) (a) calcium oxide and/or magnesium oxide with (b) an aqueous slurry of urea and a superphosphate and 20 (II) then mixing granulated urea with the resultant slurry thereby to produce the granular core.

21. A fertiliser blend of (i) a first particulate fraction where each particle contains a urea granule and a coating resulting from the use of a slurry that includes and/or has included a 25 superphosphate and urea and at least one of calcium oxide and/or magnesium oxide, and (ii) a second particulate fraction (different from (i)) of at least a superphosphate.

22. A blend of claim 20 wherein (ii) is SSP.

23. A process for providing a free flow granular fertiliser, said process comprising 30 mixing an aqueous slurry of urea and at least one superphosphate with calcium oxide and/or magnesium oxide, (optionally heating the mix and/or allowing it to rise in temperature), adding granular urea, and thereafter rendering the resultant particulate material free flow by the addition of at least one particulate calcium and/or metal oxide thereto. 35

24. A method of preparing a granular fertiliser which comprises the steps of 13 mixing an aqueous slurry of urea and at least one superphosphate with calcium oxide and/or magnesium oxide (optionally causing and/or allowing the temperature of the mix to rise), and adding granular urea thereto whilst still a slurry thereby to produce the granular fertiliser. 5

25. A method of claim 23 wherein the resultant granular is rendered free flow by the addition of at least one particulate material thereto.

26. A method of claim 24 wherein the particulate material is calcium and/or other metal oxide(s).

27. A product of a process of method of any one of claims 22 to 25. 10

28. A fertiliser blend comprising urea cored coated fertiliser blended with a phosphatic particulate fertiliser.

29. A blend of claim 28 wherein said phosphatic particulate fertiliser is a super phosphate.

30. A blend of claim 29 wherein the superphosphate is SSP.

31. A blend of any one of claims 28 to 30 having from 10 to 70 w/w of the blend of a 15 coated urea product and from 30 to 90 w/w% of the overall blend of a superphosphate.

32. A blend of claim 31 wherein coated urea fertiliser is greater than 50% w/w urea with respect to the coated granules thereof.

33. A blend of any one of claims 28 to 32 wherein the coated urea product is produced by a process as described herein with or without reference to any one or more of the accompanying 20 drawings.